Stability study and control methods for small-wattage high-intensity-discharge (HID) lamps

The increasing speed of modern power electronics opens a way to study the stability of high-intensity-discharge lamps at very-high-frequency operation. In this paper, a lamp stability study based on a simplified theory on acoustic resonance frequency distribution in a small-wattage metal-halide (MH) lamp is presented. The frequency characteristic of a low-wattage MH lamp has been analyzed. Up to 700 kHz, extensive experiments using resonant-type electronic ballast have been conducted on 35-W MH lamps to investigate different control methods for avoiding acoustic resonance. The results indicate that a randomized switching scheme cannot always eliminate are instabilities caused by acoustic resonances in small-wattage MH lamps. The stability frequency regions should be identified. A stable arc can be obtained when the lamp is operated above the highest acoustic resonance frequency.